The present invention is generally directed to an improved box beam bridge, a method of constructing an improved box beam bridge and a method of repairing an improved box beam bridge or replacing its components.
Box beam bridges are well-known in the art. The typical method used to construct box beam bridges is as follows. First, a number of box beams are constructed and positioned side-by-side so that each box beam traverses the span of the bridge. Typically these box beams include a number of transverse diaphragms located along the length of, and perpendicular to, the box beams. The transverse diaphragms include a circular hole designed to receive a post-tensioning steel cable, as described more fully below. The box beams are arranged such that the circular holes of the transverse diaphragms of adjacent box beams are aligned. Once positioned and aligned, the box beams are then secured to one another by a steel cable that travels through the circular hole of the transverse diaphragm of each box beam. This steel cable is used to create post-tensioned force in the transverse direction, which inhibits differential movement of adjacent box beams. Such differential movement can lead to cracking of the concrete deck slab that is placed on top of the box beams and/or bridge failure, e.g., by shearing the steel cable at the junction of two adjacent box beams.
Once the box beams are secured together by the steel cable and the bridge width is post-tensioned, a concrete deck slab is applied to the top portion of the bridge. This deck slab comprises the surface of the bridge. Once the deck slab is applied, the bridge is once again post-tensioned (the force being generated by the steel cable) so that the bridge and deck slab are prestressed in the transverse direction in order to resist traffic loads. At this point, grout is used to fill in any opening in the circular holes of the transverse diaphragm that remains unfilled by the steel cable. This grout is also used to cover the steel cable, in order to protect it from corrosion, and bond it to the transverse diaphragm. When hardened, this grout bonds to the steel cable, the transverse diaphragm and the circular holes therein in order to create a unitary bridge construction made up of a plurality of box beams secured together.
This typical box beam bridge construction has a number of limitations. First, the grout used to protect the steel cable from corrosion tends to deteriorate with age, resulting in a weakening of the entire bridge structure and possible corrosion of the steel cable itself. Second, the use of circular holes in the transverse diaphragms results in a number of alignment problems with adjacent box beams. Each box beam is constructed such that it has a camber, however, the camber between any two box beams may not be completely uniform. Because of variations in the camber of box beams, alignment problems between the circular holes of adjacent box beams may arise. Third, the use of grout to fill in the openings of the circular hole/steel cable junction and to protect the steel cable itself requires that the entire bridge structure be replaced when one box beam of the bridge structure becomes damaged or deteriorates. A box beam bridge structure (and a method of constructing such a box beam bridge) that addresses these limitations has yet to be satisfactorily addressed in the art.